While both rotary wing and fixed wing aircraft have been commonplace for quite some time, and although the underlying aerodynamics for each type aircraft can be separately appreciated, different combinations of the two are not so well known. Various aircraft designs which can fly both vertically and horizontally have generally fallen under the rubric of Vertical Takeoff and Landing (VTOL) aircraft. Helicopters are the most common configuration of this type and tilt rotor and tilt wing designs change the aerodynamic configuration so that the aircraft can fly both vertically and horizontally. In general, VTOL aircraft have been characterized by changes in or implementation of their respective aircraft lifting components (i.e. their airfoil and/or propulsion unit). In all cases, however, the entire fuselage of the aircraft has been directed along a linear flight path. This requirement has always been a design constraint.
In accordance with basic aerodynamic considerations, both rotary wing flight and fixed wing flight require an interaction between an airfoil and the air. Their differences stem from the fact that for fixed wing flight the airfoil is pulled or pushed through the air, along with its fuselage, in the direction of flight. On the other hand, for rotary wing flight the airfoil is rotated through the air independently of the fuselage and its direction of flight. As inferred above, we are now seeing aircraft which employ in-flight structural conversions designed to selectively benefit from the aerodynamic capabilities of either rotary wing or fixed wing flight. Heretofore, however, the fuselage has never been intentionally rotated along with its airfoil(s).
With the above in mind, a combined consideration of several basic mechanical and aerodynamic principles is important. First, all airfoils are essentially similar, and when moving through air will create a lifting force L, which can be mathematically expressed in a Lift Equation as:L=½ρSv2CLααwhere ρ is air density, S is the wing area of the airfoil, v is the airfoil velocity, α is the angle of attack of the airfoil, and CLα is the coefficient of Lift (as a function of α).
From the Lift Equation it is to be noted that for normal flight conditions only the velocity of the airfoil v, and the angle of attack of the airfoil α, are significantly controllable. Further it is to be appreciated that the airfoil will stall (i.e. L=0) when α becomes too great or v becomes too small. This is particularly important when the same airfoil will be required to provide Lift L for both rotary wing and fixed wing flight.
Another important dynamic consideration for any aircraft is its linear momentum as it moves along a linear flight path. Mathematically, linear momentum is expressed as MV, wherein M is the mass of the entire aircraft, and V is the linear velocity of the entire aircraft. Importantly, linear momentum for an aircraft will be the same, regardless of whether the aircraft is being flown in a rotary wing configuration R, or a fixed wing configuration F. The importance in both cases is that in the expression for momentum, V is a vector. Accordingly, the velocity vector V has both a magnitude (i.e. speed) and a direction. As noted above, an aircraft will have a linear momentum MV anytime it is moving along a linear path.
As is well known, the basic in-flight forces acting on an aircraft are Lift (L), Weight (W), Thrust (T) and Drag (D). Moreover, for straight and level, unaccelerated flight, L=W and T=D. With these forces in mind, another distinction between rotary wing and fixed wing flight is that for fixed wing flight, L is provided by the airfoils and T is provided by a separate mechanism (e.g. propeller, jet, or thruster). On the other hand, for rotary wing flight, L and T are both provided by the airfoil.
It is axiomatic that controls for flying an aircraft in rotary wing flight will be different than the controls used for fixed wing flight. In brief overview, first consider fixed wing flight maneuvers where the roll, pitch and yaw movements of an aircraft are more discernable. For fixed wing flight, roll is controlled by ailerons located on outboard portions of each wing. Pitch is controlled by an elevator located on the horizontal stabilizer of the aircraft's empennage, and yaw is controlled by a rudder which is located on the vertical stabilizer of the empennage. On the other hand, for rotary wing flight, aircraft maneuvers are made by controlling the thrust vector that is generated by the rotating blades.
Rotary wing flight is made possible by the combined control of collective and cyclic variation in the angle of attack a of the rotating blades. In essence, collective control provides for a same uniform increase or decrease in the angle of attack a on all rotating blades (wings). Thus, lift is provided for the aircraft. Unlike collective controls, cyclic control results from individual cyclical changes in the angle of attack a of each rotating blade during each rotation of the blade. The consequence here is that the lift vector provided by the rotating blades does more than simply provide lift. With cyclic control, the lift vector is also effectively tilted to provide a thrust component for the aircraft in the desired direction of flight.
In light of the above, it is an object of the present invention to provide an aircraft that is convertible in flight between a rotary wing configuration R and a fixed wing configuration F. Another object of the present invention is to provide an aircraft where the entire aircraft is rotated when the aircraft is in R for rotary wing flight. Still another object of the present invention is to provide a convertible aircraft which uses aileron control for pitch and roll aircraft maneuvers in its fixed wing configuration F and aileron control for both collective and cyclic control in its rotary wing configuration R.